This invention relates to a method and an apparatus for operating a steering system for a motor vehicle.
A prior art steering system is disclosed by DE-OS 40 31 316 (corresponding to U.S. Pat. No. 5,205,371) and to the extent it is relevant to understanding this invention, will be described with reference to FIGS. 1 and 2. In such a steering system the motions of the actuator 13 or 23, the motor angle .delta..sub.M, are superimposed in the auxiliary drive 12 or 22 on the steering motions imparted by the driver through the steering wheel 11 or 21, the steering wheel angle .delta..sub.L detected by the sensor 28. The total motion .delta..sub.L ' thus obtained is transmitted through the steering mechanism 14 and the steering linkage 16 to the steerable wheels 15a and 15b to set the steering angle .delta..sub.V. The actuator 13 or 23 can be an electric motor. The operating principle of such a steering system consists of determining the motor angle .delta..sub.M dependent on the steering wheel angle .delta..sub.L and dependent on signals Sm to control the dynamic behavior of the vehicle, with the steering wheel angle .delta..sub.L being determined through the sensor 28 and with the signals Sm representing vehicle motions detected by the sensors 26. The total steering angle is obtained according to the equation EQU .delta..sub.L '=.delta..sub.L /i.sub.u +.delta..sub.M,
in which the transmission ratio can be i.sub.u =1 or i.sub.u.apprxeq.1.
DE-OS 40 38 079 (corresponding to U.S. Pat. No 5,316,379) shows the superimposition of a steering component (compensating steering angle) on the front wheel and/or the rear wheel. The compensating steering angle, which depends on the differences between brake pressures, compensates for the yawing motion in the case of so-called i-split braking, i.e. braking in which the coefficients of roadway friction are significantly different on the right and left sides of the vehicle.
DE 196 01 825.0, not a prior art publication, shows a steering system that is similar to DE-OS 40 31 316 described above (corresponding to U.S. Pat. No. 5,205,371). In this case two steering components are superimposed to obtain a desired output rotational motion for the servomotor, with a first steering component serving for steering assistance, while a second steering component depends on the angular yaw rate, transverse acceleration, and/or the vehicle's longitudinal speed.
DE A1 36 25 392 shows the generation of a correction signal to a servomotor that controls the front wheel steering angle. The correction signal in this case depends on a desired-actual yaw rate difference.
GB-PS 1,414,206 shows compensation of crosswind effects by a superimposed steering angle intervention.
The purpose of this invention is to combine various control and regulation functions relating to a steering system in a suitable fashion.